Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$80.90	13.447%	$91.7786	$91.78	$91.80	$91.80
Purchase #2	$85.51	10.382%	$94.3876	$94.39	$94.40	$94.40
Purchase #3	$165.75	9.358%	$181.2609	$181.26	$181.25	$181.30
Purchase #4	$128.66	10.309%	$141.9236	$141.92	$141.90	$141.90
Purchase #5	$19.90	4.713%	$20.8379	$20.84	$20.85	$20.80
Purchase #6	$79.75	13.602%	$90.5976	$90.60	$90.60	$90.60
Purchase #7	$75.79	6.428%	$80.6618	$80.66	$80.65	$80.70
7 purchase totals =	$636.26		$701.4480	$701.45	$701.45	$701.50